“I think the president’s statement today is probably the most significant advancing of our cause since the bill-signing,” Maryland Gov. Martin O’Malley told me during a meeting in Baltimore, two hours after President Obama announced his public support for same-sex marriage. A poll out just this morning quantifies how significant. If the vote to uphold Maryland’s marriage-equality law were held today, it would pass with 57 percent of the vote. Even more compelling, 55 percent of African Americans said same-sex marriages should have the same rights as other marriages.

The poll comes from Public Policy Polling (PPP), was commissioned by Marylanders for Marriage Equality and includes an oversample of black voters (398 of 852 likely voters). And it is the first survey since Obama’s May 9 pronouncement. The PPP poll conducted a few days after O’Malley signed the bill into law in March showed 52 percent of Maryland voters would uphold it. A Post-ABC News poll from January put public support at 50 percent.

African American support has pole-vaulted. In that Post-ABC News poll, African Americans favored same-sex marriage by just 41 percent. In the March PPP poll, it was 39 percent. The 16-point swing over today’s PPP poll is remarkable and is yet more evidence of the Obama effect on blacks and their views on marriage equality.

“Things are moving in Maryland,” Josh Levin, campaign manager for Marylanders for Marriage Equality, said in a statement. “We’re approaching a supermajority who want to uphold the state’s new marriage law. The message of stronger families and basic fairness is resonating...”

Using a 2010 study of ballot measures on the legal status of same-sex couples by Patrick Egan of New York University, the new PPP poll is a very good sign for efforts in the Old Line State. According to his report, voter support for same-sex marriage bans in polls is usually seven points lower that the actual vote a ballot measure gets on Election Day. Meanwhile, the percentage of those telling pollsters they will vote against bans on same-sex marriage “tend to be relatively accurate predictors” of the results at the ballot box.

O’Malley told me earlier this month that he believed Maryland is “very fertile ground for becoming the first state to pass a referendum affirming religious freedom and marriage equality.” With 57 percent of respondents saying they would vote for Maryland’s “Religious Freedom and Marriage Equality Act,” he might be proved right.